Neuropathic pain is a type of chronic pain caused by injury or disease of the nervous system. This disorder has proven particularly difficult to treat clinically, because the fundamental mechanisms for its development and maintenance are not well understood. As a result, there is an obvious need to identify novel molecules or biological processes responsible for this pathological pain, against which new therapeutic strategies can be developed. The long-term goal of this research project is to understand the mechanisms of gene regulation critically important for the manifestation of neuropathic pain. The objective of this particular application is to identify microRNAs and their regulatory targets that play key roles in the chronic neuropathic pain condition. MicroRNAs are a new class of non-protein-coding small RNA molecules that are encoded by the genome, which regulate gene expression mainly at the post-transcriptional level and play a variety of biological functions. In particular, microRNAs have recently been implicated in the plasticity of the nervous system. Because neuropathic pain can be considered as an unwelcome consequence of the neural plasticity in the pain transmission pathways, the involvement of microRNAs in neuropathic pain is highly anticipated. The central hypothesis for the proposed research is that nerve injury induces changes in expression of particular microRNAs, which in turn regulate expression of a set of pro-nociceptive and anti-nociceptive proteins, contributing to long-lasting chronic pain states. The rationale for the proposed research is that, once particular microRNAs are identified as regulators of pain-related proteins in the neuropathic pain conditions, it would become possible to control neuropathic pain by modulating the levels of those microRNAs either pharmacologically or through molecular biological strategies. Thus, the proposed research is expected to lead to the development of fundamental knowledge that will potentially help to reduce the burdens of human disability. Based on positive preliminary data, two specific aims will be pursued. They are to: 1) identify microRNAs involved in the development and maintenance of neuropathic pain;and 2) identify target genes for the neuropathic pain-related microRNAs. For the first aim, the microarray technology and other molecular biological methods will be used to find microRNAs that show significant differences in expression levels after spinal nerve injury that causes neuropathic pain. For the second aim, the computational methods as well as histochemical approaches will be used to identify genes that are potentially regulated by particular microRNAs in the pain transmission pathways in response to nerve injury. This proposal is novel, because the possible functions of microRNAs in neuropathic pain have never been investigated. It is also significant, because it is expected to trigger a new field of research focusing on microRNA function in chronic pain, which would advance understanding of gene regulation associated with the chronic pain conditions. PUBLIC HEALTH RELEVANCE: This proposed project concerns an unexplored area of research that is expected to lead to a better understanding of the fundamental mechanisms responsible for the development and maintenance of chronic neuropathic pain. The project has relevance to public health, because once microRNA's functions in chronic neuropathic pain are identified and characterized, they would be excellent new therapeutic targets for this serious disorder.